The present invention relates generally to the field of optical communication systems, and more particularly to a method and apparatus for controlling an optical amplifier.
When utilizing optical amplifiers, in various circumstances it is desirable to control various aspects of the amplifier, such as the gain of the amplifier. For example, it may be desirable to control amplifier gain to provide an approximately stable output level despite changes in pump laser power due to, for example, pump laser aging or fiber plant losses.
Two common approaches to controlling amplifier gain are the use of logarithmic amplifiers and the use of electronic range switching. Economically acceptable implementations of these approaches typically suffer from low linearity and accuracy over all or a part of the bandwidth being amplified. In addition, these approaches typically involve a significant trade-off between bandwidth and accuracy. Generally, as bandwidth increases in these approaches, the errors associated with these approaches also increase. In addition, economically feasible implementations of these conventional approaches typically have quite limited dynamic range.
Overview
The present invention recognizes a need for a method and apparatus operable to facilitate economical amplifier gain control with increased total dynamic range. Various implementations of the present invention reduce or eliminate at least some of the shortcomings of conventional amplifier control approaches.
In one aspect of the invention, a control system for use in an optical amplifier comprises a plurality of control legs, each operable to receive one of plurality of portions of an optical signal, wherein each of the plurality of portions comprises a different percentage of the optical signal. The system further comprises a plurality of registers, each associated with one of the control legs and each operable to store a value proportional to the portion of the optical signal communicated in the associated control leg. The system also comprises a controller operable to select one of the values stored in one of the plurality of registers and to scale that value by a scaling factor to generate a scaled value, wherein the scaling factor is determined at least in part by the percentage of the optical signal associated with that value. The controller is operable to generate, based at least in part on the scaled value, a control signal operable to affect the gain of the amplifier.
In another aspect of the invention, a control system for use in an optical amplifier comprises a first optical tap operable to separate an optical signal into a primary portion comprising a first percentage of the optical signal, and a secondary portion comprising a second percentage smaller than the first percentage of the optical signal. The system also comprises a second optical tap operable to separate the secondary portion into a first control portion comprising a first percentage of the secondary portion and a second control portion comprising a second percentage smaller than the first percentage of the secondary portion. The system further includes a plurality of registers each associated with one of the control portions and each operable to store a measured value proportional to a power of the optical signal if the measured value is between a maximum value and a minimum value associated with that register. The system also comprises a controller operable to identify a register storing a measured value and to determine based at least in part on the measured value a control signal operable to affect the gain of the amplifier.
In still another aspect of the invention, a control system for use in an optical amplifier, comprises an optical tap operable to receive a feedback portion of an optical signal being amplified, to communicate a first percentage of the feedback signal to a first control leg, and to communicate a second percentage of the feedback signal smaller than the first percentage of the feedback signal to a second control leg. The system further comprises a first register operable to store a measured value of a portion of the optical signal obtained from the first control leg if the measured value does not overflow or underflow the first register, and a second register operable to store a measured value of a portion of the optical signal obtained from the second control leg if the measured value does not overflow or underflow the second register. The system still further comprises a controller operable to identify a register storing a measured value and to scale the measured value differently depending on which register stores the measured value. The controller is further operable to generate based at least in part on the scaled measured value a control signal operable to affect the gain of the amplifier.
In yet another aspect of the invention, a method of operating an optical amplifier comprises receiving a feedback portion of an optical signal and separating the feedback portion into a plurality of control portions, each comprising a different percentage of the optical signal. The method also comprises, for each control portion, storing in a register associated with that control portion a value proportional to that control portion, and selecting a register to be used to generate a control signal. The method also comprises scaling the value stored in the selected register based at least in part on the percentage of the optical signal associated with selected value, and generating the control signal based at least in part on the scaled value, wherein the control signal is operable to affect the gain of the amplifier.
Depending on the specific features implemented, particular embodiments of the present invention may exhibit some, none, or all of the following technical advantages. For example, various embodiments of the invention facilitate utilizing partitioned control circuitry to achieve high dynamic range while utilizing simple, inexpensive components that help to minimize system cost and maintain good system speed and accuracy.
Other technical advantages are readily apparent to one of skill in the art from the attached figures, description, and claims.